Previously, general BCs have been derived from the current-conservation principle
and used to study the bound-, edge-, or surface-state structures for specific continuum models:
for the 1D quadratic-in-momentum one-component model [1]} (a textbook nonrelativistic Schrödinger particle);
for the 3D quadratic-in-momentum multi-component model [2]}, in the context of semiconductors;
for the linear-in-momentum two-component model,
in the context of 2D semimetals [3]}, [4]}, 2D quantum anomalous Hall (QAH) systems [5]},
graphene [6]}, 1D insulators [7]}, and 3D Weyl semimetals [8]}, [9]};
for the linear-in-momentum four-component model of graphene [10]}, [11]}, [12]}, [13]}
and 3D Dirac materials [14]};
for the 3D quadratic-in-momentum two-component model of Weyl semimetals [15]};
for the 1D linear-in-momentum four-component model of superconductors with one Fermi surface [16]}.
